How to test in connection with Joomla ?

Nothing to test. Another tool for image compression.

@balzercomp @designbengel in this PR the images already have been optimized with imageoptim.

So, in order to test this, you should check a few of the mentioned images in multiple browsers (and maybe some older operating systems too) to make sure the optimization didn't break anything.

After @SniperSister cleared it up, i wanted to test this but i can´t find the usages of the files.
For Example: administrator/templates/isis/images/admin/featured.png, administrator/templates/isis/images/admin/filesave.png, administrator/templates/isis/images/admin/publish_x.png, administrator/templates/isis/images/admin/icon-16-deny.png

I searched with phpStorm "find in path" option... seems for me there ist some absolutely unused stuff in there ?

I'm pretty sure in Isis most of the images are unused (1.5 and 2.5 admin templates were really image heavy, Isis is mostly font icons with fewer images).

I have tested this item successfully on 4803f76

@test Tested several images in both Firefox, Chrome and Internet Explorer without any issues.

I have tested this item successfully on 4803f76

Works! A nice example that all small things count! Thanks for the PR @marcobiedermann

@RickR2H You are very welcome :)

Thanks for testing - setting RTC

@rdeutz Is there really any reason to hold back this PR until 3.5.1? Seems reducing image file size is a good optimization that should go in 3.5.0.

Beta state means only bug fixes go in, that's the procedure, that's all.

I would consider this a SEO bug since Google flags sites that don't lossly compress images.

Can we solve the conflicts please?

@marcobiedermann Can you please fix the conflicts?

This PR has received new commits.

CC: @RickR2H, @superknutsel

@Hackwar Fixed merge conflicts